One method of fabricating integrated optical components is by the deposition of doped silica waveguides formed on a doped silica film which had been deposited on a silicon substrate. This technology, referred to as "silica on silicon," has the potential to make optical devices which are smaller in size, are of greater complexity, and are potentially lower in cost than discrete optical devices which are fabricated from fiber and micro-optic components.
A variety of passive optical components have been made using silica on silicon technology in which optical waveguides are formed using a phosphosilicate glass (P-doped silica) core. In one fabrication method, the waveguides are deposited on a base layer call "hipox" formed by the oxidation of silicon under high pressure steam. The core is then covered with a thin cladding layer of SiO.sub.2. Devices built using this technology include compound Bragg reflectors, multiplexers, adiabatic polarization splitters, array star couplers and the like. In another fabrication method, doped silicon film is formed on a silica substrate.
At the present time, phosphosilicate glass core waveguides of integrated optical devices made using silica on silicon technology are normally butt coupled to input and output optical fiber by means of a bonding material such as epoxy, UV-adhesive and/or, in some instances, a potting material. The substance used to join the waveguides of the optical device to the optical fiber also serves the necessary step of filling in a gap which may exist at the butt coupling.
A current method of attaching an optical fiber to silica on silicon wafer is by first wetting the end of the fiber with a drop of suitable adhesive and then bringing the fiber into contact with the wafer. The adhesive, after drying and solidifying, holds the fiber to the wafer. The result, however, is not satisfactory for two reasons. First, the butt connection is too weak for most purposes. Second, the adhesive normally flows onto the end of an adjacent waveguide thus causing further problems when an attempt is made to attach that waveguide to an optical fiber.
The publication entitled "Fiber Attachment for Guided Wave Devices", by E. J. Murphy, Journal of Lightwave Technology, Vol. 6, No. 6, June 1988, presents a review of the status of fiber attachment to guided-wave devices. Current methods for achieving low fiber-to-waveguide-to-fiber insertion losses are discussed and techniques for aligning and permanently attaching fibers are described.
In this publication the author asserts that an appropriate bonding material and method of application is critical as it determines both the stability and reliability of the fiber-waveguide joint. He notes that UV curing adhesives are widely used because they can be cured rapidly without compromising the fiber alignment. However, UV-adhesives have questionable stability when subjected to environmental extremes in temperature, pressure or humidity and, therefore, the joints may not be sufficiently stable. Equally important, even a slight deterioration in the optical properties of the epoxy can seriously impair the transmission of optical signals through it.
The publication concludes with the statement that a major challenge of the next decade will be to develop a reliable and robust fiber attachment and packaging technology. Four years after the publication, the problems of joining an optical fiber to a silicon wafer still exist.
This invention is directed toward solving the problem of providing a reliable and robust fiber-waveguide butt coupling arrangement.